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1 Concepts of Green Chemistry. 2 Sustainable Development “...... Meeting the needs of the present without compromising the ability of future generations.

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Presentation on theme: "1 Concepts of Green Chemistry. 2 Sustainable Development “...... Meeting the needs of the present without compromising the ability of future generations."— Presentation transcript:

1 1 Concepts of Green Chemistry

2 2 Sustainable Development “ Meeting the needs of the present without compromising the ability of future generations to meet their own needs.” United Nations 1987,

3 3 Sustainable Development 1. Economic sustainability 2. Social sustainability 3. Environmental sustainability Closely related to Green Chemistry

4 4 Green Chemistry During the early 1990s,  the US Environmental Protection Agency (EPA) coined the phrase “green chemistry”  promote innovative chemical technologies  reduce or eliminate the use or generation of hazardous substances in the design, manufacture and use of chemical products

5 5 Green Chemistry Green chemistry is about the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. Environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature. Green chemistry seeks to reduce and prevent pollution at its source.

6 6 Green Chemistry can also be described as 1.Sustainable chemistry 2.Chemistry that is benign by design 3.Pollution prevention at the molecular level 4.All of the above

7 7 Green chemistry can be regarded as a reduction process. It aims at reducing the cost, waste, materials, energy, risk and hazard. Cost Energy Waste Materials Risk and hazard Reducing

8 8 The Twelve Principles of Green Chemistry: 1.Waste Prevention 2.Maximizing Atom Economy 3.Using Less Hazardous Chemical Syntheses 4.Producing Safer Chemical Products 5.Using Safer Solvents and Auxiliaries 6.Designing for Energy Efficiency 7.Using Renewable Raw Materials 8.Reducing Derivatives (fewer steps)

9 9 The Twelve Principles of Green Chemistry: 9.Using Catalysts 10.Designing Degradable Chemical Products 11.Developing Real-time Analysis for Pollution Prevention 12.Minimizing the Potential for Chemical Accidents

10 10 1.Waste prevention It is better to prevent the formation of waste than to treat or clean up the waste. Chemical wastes are undesirable products from chemical reactions. They are usually hazardous to the environment. Industrial processes should be designed to minimize the generation of waste.

11 11 2.Maximizing atom economy Traditionally, the success of a chemical reaction is judged by the percentage yield of product. It is possible to achieve 100% yield but the reaction may generate waste that is far greater in mass and volume than that of the desired product.

12 12 Consider the following reaction: AgNO 3 (aq) + KCl(aq)  AgCl(s) + KNO 3 (aq) ~100% yield undesirable Suggest reactions that have no undesirable products. Na(s) + Cl 2 (g)  2NaCl(s) N 2 (g) + 3H 2 (g)  2NH 3 (s) CH 2 =CH 2 (g) + H 2 (g)  C 2 H 6 (g) Direct combination Addition reaction

13 13 Concept of atom economy The greater the value of the atom economy, the better is the reaction to convert all the reactant atoms to the desired product.  Less waste

14 14 Calculate the atom economy of each of the following conversions C 4 H 9 OH + KBr + H 2 SO 4  C 4 H 9 Br + KHSO 4 + H 2 O 3C 4 H 9 OH + PBr 3  3C 4 H 9 Br + H 3 PO 3 = 47.0%  = 83.4% Non-S N SN1SN1  racemic mixture Greener

15 15 + 2HOCl + Ca(OH) 2 + CaCl 2 + 2H 2 O + H 2 O 2 catalyst + H 2 O 2   = 44.1% = 76.3%

16 16 + 2HOCl + Ca(OH) 2 + CaCl 2 + 2H 2 O + H 2 O 2 catalyst + H 2 O 2   Greener More harmful Less harmful harmless

17 17 3. Using less hazardous chemical syntheses Chemical syntheses should be designed to use or generate substances that possess little or no toxicity to humans and the environment.

18 18 Adipic acid is the essential feedstock for making synthetic fibres such as nylon. Consider the synthesis of adipic acid (HOOC(CH 2 ) 4 COOH). C 6 H 6 HOOC(CH 2 ) 4 COOH Traditional method C 6 H 12 O 6 HOOC(CH 2 ) 4 COOH New method

19 19 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide

20 20 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide In step 1, the starting material for the synthesis is benzene, which is a known carcinogen. The synthesis has the following risks and hazards:

21 21 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide In step 2, the oxidation of cyclohexane with air may lead to an uncontrolled reaction. It has the risk of explosion. Not all of the cobalt catalysts can be recovered. This may lead to the disposal of a heavy metal to the environment.

22 22 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide In step 3, dinitrogen oxide or nitrous oxide (N 2 O) gas is produced as a by- product. It is a greenhouse gas with an effect which is 200 times the effect of carbon dioxide.

23 23 biosynthetic pathway D-glucose (1) E. coli 3-dehydroshikimic acid (3) Pt/H 2, 3  4 atm muconic acid adipic acid (2) E. coli Much greener 1. the starting material, glucose, is harmless. shikimic acid 1 2 3

24 24 biosynthetic pathway D-glucose (1) E. coli 3-dehydroshikimic acid (3) Pt/H 2, 3  4 atm muconic acid adipic acid (2) E. coli Much greener 2.E. coli is used to catalyse two steps of the reaction. This reduces the use of certain chemical reagents with significant toxicity.

25 25 biosynthetic pathway D-glucose (1) E. coli 3-dehydroshikimic acid (3) Pt/H 2, 3  4 atm muconic acid adipic acid (2) E. coli Much greener 3.there are no by-products generated during the synthesis.

26 26 4. Producing safer chemical products The chemical products synthesized should be safe to use. For example, chemicals called organotin compounds(Anti-biofouling agent) were used in large ships to prevent accumulation of barnacles( 藤壺 ) and marine plants traditionally.

27 27 The accumulation of barnacles( 藤壺 )on the ship may increase the resistance to its movement.

28 28 However, organotin compounds are highly toxic to the surrounding marine life. Then, Rohm and Haas Company developed a non-toxic alternative called Sea-Nine TM. It degrades quickly in the marine environment and is not toxic to the surrounding marine life.

29 29 5. Using safer solvents and auxiliaries The solvents and auxiliaries (e.g. drying agent, blowing agent, etc.) used in chemical syntheses will become part of the wastes. They may cause environmental pollution and health hazard.

30 30 CFCs : - unreactive volatile liquids or easily liquefied gases low flammability low toxicity  Cleaning solvents Propellants Refrigerants Blowing agents They were eventually banned because they deplete the ozone layer.

31 31 Screening of UV radiations by ozone layer = nm =250 nm ~99% of UV radiation from the sun are screened out

32 32 They were eventually banned because of their ability to deplete the ozone layer. One Cl  free radical can destroy ozone molecules Cl  + O 3 → ClO + O 2 ClO + O 3 → Cl  + 2O 2 CFCl 3 → CFCl 2 + Cl  uv chain reaction

33 33 Nowadays, CO 2 is used to replace CFCs as the blowing agent. CO 2 is non-toxic and non-flammable. It does not deplete the ozone layer. STYROFOAM produced with carbon dioxide as the blowing agent

34 34 Many solvents currently used in the chemical industry are harmful and volatile They are known as Volatile Organic Compounds (VOCs) E.g. Propanone, benzene, dichloromethane, dibromomethane, chloroform and carbon tetrachloride. VOCs + NO x photochemical smog UV

35 35 Use safer solvents and auxiliaries – How? A.Use of water as an environmentally innocuous solvent; B.Use of liquid or supercritical carbon dioxide; C.Use of non-volatile solvents: ionic liquids; D.Use of hybrid solvent systems of the three above; E.Solvent-less reactions;

36 36 A.Aqueous Media as Solvents for Chemical Synthesis and Processes. Advantages: – Non-toxic – Non-flammable – Inexpensive – Environmentally benign Disadvantages: – Many organic compounds are not soluble in water

37 37 B.Use of liquid or supercritical carbon dioxide Examples 1.Decaffeination 2.Extraction of essential oil

38 38 Using supercritical CO 2 as solvent in decaffeination T /  C P / atm Solid Liquid Vapour A T B C P c = 73atm T c = 31  C Gas Supercritical fluid CO 2

39 39 Using supercritical CO 2 as solvent in decaffeination Coffee beans decaffenation with caffeine without caffeine In the past, solvents used for decaffeination are harmful to the environment and human beings E.g. CHCl 3, CH 2 Cl 2, benzene

40 40 Advantages of decaffeination using scCO 2 Supercritical CO 2 has 1.the high diffusion of a gas that allows it to penetrate deep into the beans 2.the high density of a liquid that dissolves 97–99% of the caffeine Coffee beans Supercritical CO 2 with caffeine without caffeine

41 41 Advantages of decaffeination using scCO 2 Will not reinforce the greenhouse effect since scCO 2 comes from the atmospheric CO 2 Coffee beans Supercritical CO 2 with caffeine without caffeine

42 42 Limitations and disadvantages of decaffeination ? 1.Decaffeination is based on solvent extraction (principle of partition equilibrium).  complete removal of caffeine is not possible 2.Other compounds are lost during the process.  the flavor and aroma are changed.

43 43 Essential oils are organic compounds that are extracted from natural sources and used in many products such as flavorings, fragrances, and cleaning products. D-limonene Orange peel D-limonene : - optically active - difficult to prepare *

44 44 Traditionally, it was done by organic solvent extraction or steam distillation D-limonene Orange peel Disadvantages : - VOCs used in solvent extraction are harmful to the environment -More energy is consumed in steam distillation

45 45 Liquid CO 2 can be obtained easily by allowing dry ice to evaporate in a closed vessel at room temperature. D-limonene Orange peel Liquid CO 2 ~5.1 atm

46 46 Liquid CO 2 is easily obtained due to the low pressure at the triple point T /  C P / atm Solid Liquid Vapour A T B C P c = 73atm T c = 31  C Gas Supercritical fluid CO atm

47 47 C.Using ionic liquids as solvents Low m.p. due to poor packing between ions of significantly different sizes High b.p. due to ionic nature  Low volatility E.g.

48 48 By modifying the structures and charges of the ions, More viscous ionic liquids can exhibit specific properties such as m.p., viscosity, volatility & hydrophobicity to meet the particular needs of a synthesis. Designer solvents

49 49 Advantages of using ionic liquids over using VOCs as solvents (2010 AL Paper 1 Q.6) 1.Tailor-made 2.High b.p. Not easily escape to the environment Volatile organic reactants/products can be easily removed by simple distillation. The solvents can be easily recycled and reused 3.Low flammability due to their low vapour pressure

50 50 Advantages of using ionic liquids over using VOCs as solvents 4.Wide liquid range due to low m.p. and high b.p. Organic syntheses can occur at higher temperatures 5.Ionic nature can allow organic syntheses involving ionic species.

51 51 E.Solvent-less reactions Not easy for reactions involving heating as heat exchange is difficult without a solvent Solved by microwave heating Suitable only for polar reactants which are active to microwave.

52 52 6.Designing for energy efficiency Chemical syntheses should be designed to minimize the use of energy. heat liquid mixtures for separating and purifying products by distillation. Energy is used to raise the temperature of reactants so that a reaction starts or goes on.

53 53 CATALYTIC CHAMBER (450  C) heat upcool down N 2 & H 2 hot compressed N 2 & H 2 NH 3, unreacted N 2 & H 2 HEAT EXCHANGER N 2 (g) + 3H 2 (g) 2NH 3 (g) 450  C, 200 atm Finely divided Fe  H < 0

54 54 Using catalysts - reactions at lower T & P Using microwave heating - more efficient Using biosynthetic pathways - reaction at ambient T & P Ways to conserve energy:

55 55 Class practice 52.3 Class practice stage fermentation process Fermentation Glucose KGA (an intermediate compound) KGA (an intermediate compound) Sorbose Sorbitol Vitamin C Reichstein process Fermentation Chemical synthesis Glucose DAKS (an intermediate compound) DAKS (an intermediate compound) Sorbose Sorbitol Vitamin C Greener

56 56 7. Using renewable raw materials They are often made from agricultural products. E.g. glucose for making adipic acid and vitamin C biodiesel for motor vehicles Renewable raw materials

57 57 vegetable oil methanol biodiesel glycerol KOH renewable Diesel comes from petroleum which is non-renewable Burns more completely than diesel due to its higher oxygen.

58 58 In the production of synthesis gas, natural gas is used as the raw material for the steam-methane reforming process. From natural gas Synthesis gas (or syngas) CH 4 (g) + H 2 O(g) 3H 2 (g) + CO(g) 700  1000°C, 10  20 atm NiO

59 59 N 2 (g) + 3H 2 (g) 2NH 3 (g) 450  C, 200 atm Finely divided Fe 2H 2 (g) + CO(g) CH 3 OH(g) 250°C, atm Cu/ZnO/Al 2 O 3 CH 3 OH(g) + CO(g) CH 3 COOH(g) Ir based catalyst, HI Cativa process From natural gas Synthesis gas (or syngas) CH 4 (g) + H 2 O(g) 3H 2 (g) + CO(g) 700  1000°C, 10  20 atm NiO

60 60 In the production of synthesis gas, natural gas is used as the raw material for the steam-methane reforming process. Natural gas Non-renewable raw material Landfill methane gas Pig’s manure Paper & wood waste Seaweed Renewable raw materials Replaced by

61 61 Shredded paper (left) and seaweed (right) can be used as the raw materials for the production of synthesis gas

62 62 8. Reducing derivatives We should avoid unnecessary use of synthetic steps in order to reduce the derivatives of the desired product. Otherwise, more reagents are needed and more waste will be generated.

63 63 Na 2 WO 4 as catalyst [CH 3 (n-C 8 H 17 ) 3 N]HSO 4 as phase transfer agent  C, 8h 30% 93% yield 1.One-step synthesis with high yield 2.Proceeds in aqueous medium at relatively low T 3.Reagents and by-product are environmentally benign Sato, K.; Aoki, M.; Noyori, 1998 A “Greener” Route to Adipic Acid.

64 64 9. Using catalysts Bleaching of wood pulp in paper manufacturing Reaction 1 is greener because it has a higher atom economy it involves less harmful chemicals 1. H 2 O 2 + dye H 2 O + (dye + O) 2. OCl  + dye Cl  + (dye + O)

65 65 9. Using catalysts Bleaching of wood pulp in paper manufacturing Bleaching with Cl 2 may lead to the formation of dioxin which is an accumulative carcinogen 1. H 2 O 2 + dye H 2 O + (dye + O) 2. OCl  + dye Cl  + (dye + O)

66 66 H 2 O 2 + dye H 2 O + (dye + O) TAML TM catalyst - non-toxic iron-based ‘green’ catalysts. Tetra-Amido Macrocyclic Ligand (TAML) - promote the conversion of hydrogen peroxide into hydroxyl radicals that are involved in the bleaching process - catalyse the oxidation of organic substances in wastewater.

67 67 TAML TM catalysts can be used to clean up wastewater streams in the pulp and paper industry

68 68 Environmental benefits of using TAML TM catalysts in wastewater treatment Decrease in energy requirements Elimination of chlorinated organic substances Reduction in water usage Degradable catalysts

69 Designing degradable chemical products Many chemical products persist in the environment after use. They should be designed so that they can be broken down into harmless substances.

70 70 E.g. DDT, they accumulate in plants and animals, causing damage to the final consumers  humans. Designing degradable pesticides that can be decomposed by water, sunlight or micro-organisms. Pesticides

71 71 Degradable Plastics Several types of degradable plastics:  biopolymers  photodegradable plastics  synthetic biodegradable plastics

72 72 Biodegradable plastic utensils. Photodegradable plastic bag.

73 Developing real-time analysis for pollution prevention When coal is burnt in industrial boilers, SO 2 (a pollutant) is formed. Real-time monitoring system for monitoring sulphur dioxide (SO 2 ) level If the temperature of the boilers is too high, a large amount of SO 2 will be generated.

74 74 Real-time monitoring system for monitoring sulphur dioxide (SO 2 ) level Once it reaches an unacceptable level, an alarming signal will be generated. Then the temperature will be lowered immediately. Using real-time monitoring, the amount of SO 2 generated can be measured all the time.

75 Minimizing the potential for chemical accidents Chemical accidents include leakages, explosions and fires. Minimize the use of volatile liquids or gases which are associated with the majority of chemical accidents. If possible, allow reactions to proceed under ambient T & P.


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